In the commercial production of acrylonitrile, propylene is ammoxidized to acrylonitrile by contacting a mixture of propylene, ammonia and oxygen with a fluid-bed catalyst. A gross reaction product is produced which contains various components in addition to acrylonitrile such as N.sub.2, CO, CO.sub.2, H.sub.2 O, unreacted propylene, hydrogen cyanide, acrolein, acetone, acetonitrile, acetaldehyde, etc.
The first step in recovering acrylonitrile from this gross reaction product is to separate the product into liquid and vaporous phases. This is accomplished by cooling the reaction product to condense higher boiling components. Cooling can be accomplished either by indirect heat exchange or by direct contact with water.
The liquid phase produced by the above procedure contains product acrylonitrile, acetonitrile, HCN and minor amounts of organic impurities. It is subjected to further processing to recover acrylonitrile, acetonitrile and HCN. The gaseous phase produced by the above technique contains roughly 85% N.sub.2, 1 to 2% O.sub.2, 1 to 2% propane, about 0.1 to 0.5% propylene, 3 to 6% CO.sub.2, 2 to 3% CO and 3 to 5% H.sub.2 O.
Because of the propylene and propane in the gaseous phase, it cannot be simply discharged to the atmosphere. Rather, it is normally incinerated whereby the propylene and propane are converted to carbon monoxide and carbon dioxide. This is disadvantageous because valuable propylene is lost.
Accordingly, it is an object of the present invention to provide a new technique for processing the gaseous phase produced in the recovery of acrylonitrile from the fluid-bed ammoxidation of propylene which advantageously utilizes the propylene in the gaseous phase.